Last year we reported that uteroglobin (UG) in conjunction with transglutaminase can render implanting embryonic cells non-antigenic to maternal lymphocytes. We proposed at that time that the presence of uteroglobin and transglutaminase in the prostate may be responsible for creating a non-antigenic state of the male gamete in the female organism. We have now tested the hypothesis by mixing epididymal sperm with female lymphocytes with various treatment combinations with uteroglobin, transglutaminase or its inhibitors and antibodies. Our results indicate that epididymal sperm is highly antigenic to female lymphocytes. However, treatment of these sperm with prostatic fluid, or uteroglobin and transglutaminase makes them non-antigenic. Inhibition of transglutaminase abolishes the immunosuppressive role of uteroglobin and prostatic fluid. These findings further substantiate our hypothesis that protein such as UG in the prostate may crosslink with antigens of the sperm surface to mark their antigenicity.